There was a number of reasons. The articles of confederation didn't enable the central government to collect taxes. There was no National court to solve international conflicts. And many states took advantage of a missing strong leading figure in the form of a president. The Articles of Confederation was week due to giving too much power to the central government.
Nationalism is a social, political, and economic system. Devotion, especially excessive or undiscriminating devotion, to the interests or culture of a particular nation-state. The belief that nations will benefit from acting independently rather than collectively, emphasizing national rather than international goals.
